Leslie Gains-Germain, Montana State University, M.S. Statistics Candidate
Data from Alaska Department of Fish and Game
Question 1: Is there evidence that the distance Seward charter boats travel to fish for bottomfish has changed over the years 1993-2014?
Question 2: Is there evidence of a change in the mean length of halibut caught by Seward fishermen over the years 1994-2013?
| abbreviation | description |
|---|---|
| H | halibut exclusively |
| B | any combination of bottomfish (halibut, rockfish, lingcod, Pacific cod, sharks) |
| B+S | any combination of bottomfish and salmon (e.g. halibut+coho) |
The odds of fishing in Cape Cleare in \(2014\) are estimated to be \(2.43\) times the odds of fishing in Cape Cleare in \(1993\), with a \(95\%\) confidence interval from \(1.22\) to \(4.92\) times.
The odds of NOT fishing in Resurrection Bay in \(2014\) are estimated to be \(2.78\) times the odds of NOT fishing in Resurrection Bay in \(1993\), with a \(95\%\) confidence interval from \(1.32\) to \(5.82\) times.
| port | sector | date | age | length | sex | statarea | length.in | area |
|---|---|---|---|---|---|---|---|---|
| Seward | Charter | 5261994 | 11 | 120.0 | F | 495938 | 47.24 | resbay |
| Seward | Charter | 5261994 | NA | 128.0 | F | 475934 | 50.39 | capecleare |
| Seward | Charter | 5261994 | 13 | 85.0 | M | 475934 | 33.46 | capecleare |
| Seward | Charter | 5261994 | 13 | 85.5 | M | 475934 | 33.66 | capecleare |
| Seward | Charter | 5271994 | 11 | 126.5 | F | 485935 | 49.80 | junken |
| Seward | Charter | 5271994 | 11 | 95.8 | F | 475934 | 37.72 | capecleare |
In the waters around Cape Junken, there is strong evidence of a relationship between mean fish length, on the log scale, and time over the years \(1994\) to \(2013\) (two-sided p-value\(<0.0001\) from t-stat\(=-5.520\) on \(18\) df).
The median halibut length in Cape Junken is estimated to have decreased by \(16.5\)% over the years \(1994\) to \(2013\), with a \(95\)% confidence interval from a \(11.0\)% to a \(21.6\)% decrease.
Technically does not extend to all Seward boats/fish,
BUT....
No causal
There is moderate evidence that the log odds of fishing at Cape Cleare changes over time, assuming a linear trend over years \(1993\) to \(2014\) (p-value\(=0.02479\) from drop-in-deviance F-stat\(=5.89\)).
| YEAR coef | SE | F-stat | Pr(>F) | |
|---|---|---|---|---|
| capecleare | 0.0404 | 0.0161 | 5.891 | 0.0248 |
| resbay | -0.0463 | 0.0171 | 7.351 | 0.0134 |
| nuka | 0.0188 | 0.0385 | 0.238 | 0.6309 |
| patton | 0.0760 | 0.0200 | 12.532 | 0.0021 |
Each area modeled separately